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The effect of intermediate annealing between cold rolled steps on crystallographic texture and magnetic properties of Fe–2.6% Si
Journal of Magnetism and Magnetic Materials 362 (2014) 141–149
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Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
The effect of intermediate annealing between cold rolled steps on crystallographic texture and magnetic properties of Fe–2.6% Si M.Z. Salih a,n, B. Weidenfeller c, N. Al-hamdany a, H.-G. Brokmeier a,b, W.M. Gan b a
Institut für Werkstoffkunde und Werkstofftechnik, TU Clausthal, Agricolastraße 6, D-38678 Clausthal-Zellerfeld, Germany Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, D-21502 Geesthacht, Germany c Institut für Elektrochemie, Abteilung für Materialwissenschaft, Arnold-Sommerfeld-Strasse 6, D-38678 Clausthal-Zellerfeld, Germany b
art ic l e i nf o
a b s t r a c t
Article history: Received 2 December 2013 Received in revised form 23 February 2014 Available online 17 March 2014
The crystallographic textures and magnetic properties of Fe–2.6 wt% Si after two different cold rolling and thermal treatment processes were investigated. The first set of samples was 90% cold rolled and annealed for 20 min at 600 1C, 700 1C, 900 1C and 1100 1C, while the second set was cold rolled for 75% and 60% with intermediate annealing at 600 1C for 60 min. Samples were analyzed by neutron diffraction and magnetic measurements. By means of the one and two stage cold rolling processes important cube (0 0 1)[1 0 0] and Goss components {1 1 0}〈0 0 1〉 were produced. Magnetic properties obtained through the two stage process were better than the properties found with the one stage process due to a higher fraction of the cube and Goss components in the material after the two stage process. An increase of grain sizes does not lead to better magnetic properties. & 2014 Elsevier B.V. All rights reserved.
Keywords: Electrical steel Hot rolling Cold rolling Intermediate annealing Magnetic property Neutron diffraction
1. Introduction Silicon steels are used in electrical machinery, like motors, generators and transformers. The magnetic materials used for technological applications can be divided into hard and soft magnetic materials. Hard magnetic materials are characterized by the highest possible energy product or the highest possible coercive force, whereas soft materials require the lowest coercive force or the highest permeability. All these properties are anisotropic and dependent on the texture in the polycrystalline state [1]. Iron based materials with the cube component (0 0 1)[1 0 0] provide the best soft magnetic properties such as high permeability, low power loss and low coercive force. This kind of texture can be obtained in Fe–Ni alloys. However, in Fe–Si alloys the cube component is difficult to produce while the Goss component (1 1 0)[0 0 1] is easier [1,2]. The improvement of texture for non-oriented electrical steels during thermo-mechanical processing can be attained by reducing the intensity of undesirable components such as α fiber (〈1 1 0〉//RD), γ fiber (〈1 1 1〉//ND), and {h h l}〈h/lþ1 h/lþ2 h/l〉 and increasing the fraction of spread along the η fiber (〈1 0 0〉//RD) and θ fiber (〈1 0 0〉//ND). These fibers are related to the macroscopic axis of the
n Correspondence to: Institut für Werkstoffkunde und Werkstofftechnik, Agricolastrasse 6, 38678 Clausthal-Zellerfeld, Germany. Tel.: þ49 4152 87 2635; fax: þ 49 4152 87 2666. E-mail address: [email protected] (M.Z. Salih).
http://dx.doi.org/10.1016/j.jmmm.2014.03.009 0304-8853/& 2014 Elsevier B.V. All rights reserved.
sample, defined as the rolling direction (RD), transverse direction (TD) and normal direction (ND) [3–6]. The two important components (0 0 1)[1 0 0] (cube) and {1 1 0}〈0 0 1〉 (Goss) can be obtained by hot rolling, cold rolling and cold rolling with intermediate heat treatments. There are two processes that can produce sheets with a Goss texture. The first one is cold rolling in two stages of about 70% and 50% reduction with intermediate annealing whereupon a hot band containing MnS precipitates is observed. In the second process a hot band containing additional AlN precipitates is subjected to cold rolling in one stage to about 85% followed by primary recrystallization [7]. The effects of the two different cold rolling processes of Fe–2.6% Si (one stage and two stages with various intermediate annealing processes) on the crystallographic texture and the magnetic properties are studied. The crystallographic texture was examined by neutron diffraction and the magnetic properties were measured using a hysteresis measurement system. Due to the coarse grain structure of the materials after annealing processes at high temperature high penetration and large beam cross section of neutron diffraction is an efficient tool for analysis of the bulk texture for these polycrystalline materials [8–10].
2. Materials An iron silicon alloy with 2.6 wt% silicon hot rolled at 1100 1C was provided by VACUUMESCHMELZE (Hanau, Germany) with a
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thickness reduction from about 330–380 mm to 10 mm. This corresponds to a reduction of approximately 97%. The chemical composition of the material (Table 1) was determined by electric discharge spectroscopy (Spectro Analytical Instrument, GmbH) after hot rolling. Samples of 25 mm 55 mm 10 mm were cut from the hot rolled band and afterward cold rolled on a laboratory mill (BÜHLER, Germany) to a final thickness of 1 mm along a direction perpendicular to the previous hot rolling direction (CRD? HRD). Reduction steps in the cold rolling processes were 0.1 mm/step. Two different rolling processes were used as shown schematically in Fig. 1.
2.1. Pole figure measurement The measurement of pole figures using neutrons was carried out using the materials science diffractometer (STRESS-SPEC) at the FRM2@MLZ (Garching, Germany) [11,12]. Fig. 2 shows a layout of the STRESS-SPEC with the sample mounted on the robot arm using the continuous scanning mode for intensity collection of complete pole figures. Continuous scanning is much faster than the step scan mode and allows, in parallel, the optimization of pole figure resolution on the grids. The sample dimensions for neutron measurements are 10 10 10 mm3. These dimensions increase the gage volume and improve the grain statistics which are needed for the coarse grained material after annealing. Therefore 10 slices were cut from the 1 mm thick sheet with a marked RD and glued together, using the spherical sample method of Tobisch and Bunge [13]. The average texture of the whole sample can be obtained by a large cross section of the beam, in our case 25 mm2 (see Fig. 3a). The measurements were carried out with a pyrolytic graphite monochromator (PG) and a monochromator take off angle which allows us to work with PG(004) and PG(006) planes. The main advantage in using two wavelengths is that the counting time in getting all needed pole figures with one detector setup is saved. The used area
detector of 300 300 mm² gave the Fe (1 1 0) reflection with PG(004) and Fe (2 0 0) and Fe (2 1 1) with PG(006) (Fig. 3b). The STRESS-SPEC diffractometer is equipped with a sample magazine which can be handled automatically by the robot enabling the measurement of all samples of each treatment without manual sample changing. Therefore, one of the advantages of this robot system is the operation of an automatic sample changer. Pole figure collection for one sample was done in about 1.2 h to get 72 readouts during continuous rotation and 6 tilt angles due to the detector size. The software package StressTextureCalculator (STeCa) [14] has been used to extract pole figure data from the area detector using the mathematical formulation of Bunge and Klein [15]. The Orientation Distribution Function (ODF) was calculated from three complete pole figures (1 1 0), (2 0 0) and (2 1 1) by ISEM (Iterative Series Expansion Method) up to a degree of series expansion Lmax ¼22 [16]. 2.2. Measurement of magnetic properties Samples for magnetic measurement were rectangular bars with a sample volume of 1 1 25 mm3. Measurements were conducted
Table 1 Results of the chemical composition of the used 97% hot rolled samples. Material
%Si
%C
%Mn
%S
%N
%Al
Fe–Si
2.6
0.0079
0.1135
0.0033
0.0065
0.001 Fig. 2. Stäubli RX160 robot with mounted sample.
hot rolling at 1100°C
Annealing at 800°C/ 60 min
Annealing at 600°C/ 60 min heating Cooling 4°C/ min 1.2°C/ min
heating 6°C/ min 75% cold rolling 200°C
200°C
60% cold rolling
Annealing at 1100°C/ 20 min
90% cold rolling
900°C/ 20 min 700°C/ 20 min 600°C/ 20 min
Fig. 1. Schematic presentation of the processing parameters.
Cooling 1.3°C/ min
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Diffracted
143
λ1= 1.8 Å 110
beam
Primary beam λ2= 1.2 Å 200
Samples
λ2= 1.2 Å 211
Fig. 3. (a) Schematic view of the measurement setup and (b) diffraction image with two wavelengths.
with a digital hysteresis recorder, described in detail elsewhere [17]. For purposes of comparability of the magnetic sample's properties, measurements have been conducted at identical polarizations and magnetizing frequencies by varying the magnetic field strength.
Table 2 Selected magnetic properties of the investigated samples which were cold rolled at one stage, cold rolled at two stages with an intermediate annealing process and annealed samples. Properties are measured in the rolling direction.
3. Results and discussion 3.1. Magnetic properties Table 2 shows variation of the magnetic properties of Fe–2.6% Si samples for one stage cold rolling and two stage cold rolling with an intermediate annealing process, measured at the magnetizing frequencies of 10 Hz and 50 Hz and a maximum polarization of J0 ¼1.8 T. The saturation polarization was estimated to be Js ¼ 2.04 T which corresponds to the values found in the literature for Fe–2.6% Si [18]. As can be seen in Table 2 power losses increase with frequency. This is due to an increase of classical and anomalous losses which are frequency dependent [18]. Relative to eddy currents in the sample the permeability is slightly decreased. Permeability values measured in the rolling direction of the as-received samples are nearly twice the values measured in the transversal direction. This indicates anisotropy of the grains oriented with magnetic easy axis in the rolling direction. Astonishingly the cold rolling process changes the permeability to higher values and simultaneously the power losses and coercive forces to lower values. Usually the rolling process induces many dislocations such that the permeability is decreased and coercive forces and power losses are increased. This is not the case here and therefore it can be assumed that the dislocation density in the asreceived material is similar to that in the material after the cold rolling process. Furthermore, these results lead to the assumption that the cold rolling process after the first hot rolling process causes a preferred crystallographic orientation of the grains resulting in better magnetic properties. This effect is higher for the 75% cold rolled materials than for the 90% cold rolled alloys. For one stage cold rolling the annealing process further increases the permeability values and decreases power losses and coercive forces. Regarding the values in Table 2 the thermal treatment of 20 min at 900 1C seems to lead to an optimum value in magnetic properties in the investigated range. According to Fig. 4 the mean grain size in such samples is around 122 μm. A further increase of the grain sizes by higher annealing temperatures does not lead to lower coercive force or power loss and higher permeability values although the number of imperfections in the material is reduced. This behavior is well known as the so-called Brown's paradoxon [19]. Impurities like dislocations and grain boundaries are sources for magnetic stray
As-received RD As-received TD
Permeability Power loss (kJ/m3)
Coercive force (A/m)
10 Hz 50 Hz 10Hz
50 Hz
10 Hz
50 Hz
76 47
74 46
3.1 1.3
11.76 2.42
435 155
1758 386
One stage cold rolling 90% Cold rolling 77 Annealing at 600 1C/20 min 89 Annealing at 700 1C/20 min 105 Annealing at 900 1C/20 min 112 Annealing at 1100 1C/20 min 49
76 89 101 112 49
3.1 1.31 1.01 0.74 0.98
4.21 2.39 2.02 1.43 2.70
420 148 142 101 113
640 366 329 269 401
Two stage cold rolling 75% Cold rolling Annealing at 600 1C/60 min 60% Cold rolling Annealing at 800 1C/60 min
93 122 82 130
2.89 1.32 2.96 1.1
3.62 2.23 3.57 1.86
323 171 420 108
526 355 570 266
92 116 84 121
fields. The energy stored in these magnetic stray fields can be reduced by the nucleation of domain walls. The higher number of magnetic domain walls leads to a reduction of power loss during magnetization reversal [20]. The two stages of cold rolling with an intermediate annealing process lead to an increase in the permeability values and simultaneously to a decrease of power losses and coercive forces. Regarding the values in Table 2 the annealing process at 800 1C/ 60 min shows the highest increase in the permeability and the biggest decrease in power losses and coercive forces compared to the other thermal annealing processes including the ones from the one stage cold rolling. According to Fig. 11, the mean grain size in such samples annealed at 800 1C/60 min is around 75 μm.
4. Texture 4.1. One stage cold rolling plus different annealing temperatures The main types of microstructures in the heavily deformed materials that could be related to different texture components include at first a “smooth” microstructure containing orientations between (0 0 1)[1 1 0] and (112)[1 1 0] with continuous orientation changes between neighboring areas. In this type, a continuous spread of (0 0 1)[1 1 0] toward (0 0 1)[1 0 0] exists. The second
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Fig. 4. Optical microscopy of (a) 97% hot rolled, (b) 90% cold rolled, (c) 600 1C/20 min (average grain size 19 mm) annealed, (d) 700 1C/20 min (average grain size 20 mm) annealed, (e) 900 1C/20 min (average grain size 122 mm) annealed and (f) 1100 1C/20 min (average grain size 354 mm) annealed samples.
Fig. 5. (a) φ2 ¼01 and (b) φ2 ¼ 451 ODF sections in Euler space showing the main texture components in steel.
type of microstructure consists of “grooved” regions, which are composed of orientations of the 〈1 1 1〉||ND family, mainly the orientation (1 1 1)[2 1 1] [21,22]. The microstructure of the hot rolled samples shows a mixture of smooth type and grooved type and changes after 90% cold rolling to smooth type in the heavily deformed material. The average grain sizes in the (rolling, transverse and normal) directions were calculated by the line intercept method and are given in Fig. 4. The microstructure after recrystallization shows coarse equiaxed grains as can be seen in Fig. 4. Furthermore, it can be seen that the texture changes after 90% cold rolling. The hot rolling components are rotated as was expected from the literature [23] and the cross rolling results in a very strong {0 0 1}〈1 1 0〉.
The most common texture components and orientation fibers in steel after rolling and recrystallization, which are shown in Fig. 5, are the φ2 ¼01and φ2 ¼ 451 sections of the ODF. According to the 451 section (see Fig. 5b), three different fibers (θ fiber 〈0 0 1〉||ND, α fiber 〈1 1 0〉||RD and γ fiber 〈1 1 1〉||ND) and also the Goss {1 1 0}〈0 0 1〉 component as shown in Fig. 6 can be observed. These fibers appeared due to the hot rolling processes [25]. Due to the cutting process of the 97% hot rolling sample the former RD becomes the TD and consequently the starting texture for cold rolling changes as shown in Fig. 7. The magnetic properties presented in Table 2 are related to the new sample orientation. It has to be noticed that the θ fiber 〈1 0 0〉||ND has not changed but the Goss component has changed. According to the ODF section
M.Z. Salih et al. / Journal of Magnetism and Magnetic Materials 362 (2014) 141–149
145
φ1
RD Ф
TD
Contours 1 2 3 5 F max = 6.0 mrd
110 Pmax= 2.7 mrd
Fig. 6. (a) (1 1 0) pole figure and (b) ODF for 97% hot rolling direction at φ2 ¼01 and φ2 ¼ 451.
RD φ1 Ф
TD
110 Pmax= 2.7 mrd
Contours 1 2 3 5 F max = 6.0 mrd
Fig. 7. (a) (1 1 0) pole figure and (b) ODF for as-received 901 rotated at ND at φ2 ¼ 01 and φ2 ¼451.
RD
φ1 Ф
TD
110 Pmax= 7 mrd
Contours 1 10 15 25 30 F max = 32.7 mrd
Fig. 8. (a) (1 1 0) pole figure and (b) ODF for 90% cold rolling at φ2 ¼ 01 and φ2 ¼451.
at φ2 ¼451 (see Fig. 5b) after rotated the sample 901 caused the position of Goss component is changed at the Euler angles of the orientation (φ1,Φ, φ2) (901, 901, 451) to the new position component (1 1 0)[1 1 0] at (01, 901, 451). During the cold rolling process the crystallite orientations which were primarily produced in the hot rolling process are rotated as expected [23]. Such a cross rolling procedure produces a very strong {0 0 1}〈1 1 0〉 texture, which can be seen in Fig. 8. It is developed due to a rotation of 901 around the ND. All 〈1 1 0〉 fibers parallel to the rolling direction are transferred into [1 1 0] fibers parallel to the transversal direction of the hot rolling step, and the
subsequent 90% cold rolling process finally converts them to a rotated cube component (0 0 1)[1 1 0] [24]. Fig. 9 shows the evolution of the texture after 90% cold rolling and subsequent annealing of the sample at different temperatures (600 1C, 700 1C, 900 1C and 1100 1C) for 20 min. During the primary recrystallization annealing at 600 1C, a homogeneous intensity spreads along the α fiber; the αn fiber and the γ fiber can be observed. After annealing of the sample at 700 1C, an intensity spreads along the α fiber higher than along the γ fiber, particularly increasing at the Euler angles of the orientation (φ1,Φ, φ2)E (15, 35, 45) that is visible. These angles correspond
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approximately to the (112)[7 11 2] set of miller indices [27]. This local maximum lies on a secondary fiber parallel to the α fiber (〈1 1 0〉||RD), running from the (1 1 1)[1 1 2] components to the
cube fiber. The annealing of the samples at 900 1C results in a high intensity spread along the α fiber and particularly a stronger intensity of the (1 1 2)[7 11 2]. The results also show that all the
600°C
700°C
900°C
1100°C
Fmax= 5.7 mrd Contours 1 2 3 5
Fmax= 7.6 mrd Contours 1 2 3 5 7
Fmax= 12.3 mrd Contours 1 2 4 8 10 12
Fmax= 8.5 mrd Contours 1 2 3 5 7 9
φ2 = 0°
φ2= 45°
Fig. 9. Annealing texture of one stage cold rolling process by φ2 ¼ 01 and φ2 ¼451 ODF sections after annealing at 600 1C, 700 1C, 900 1C and 1100 1C for 20 min.
Fig. 10. The α, γ, η and ε fibers of the one stage cold rolling process after annealing at 600 1C, 700 1C, 900 1C and 1100 1C for 20 min.
M.Z. Salih et al. / Journal of Magnetism and Magnetic Materials 362 (2014) 141–149
components that have spread along the γ fiber diminished and only the (1 1 1)[1 1 2] component has appeared. An annealing of the samples at 1100 1C leads to a significant increase of the intensity spread along the α fiber (〈1 1 0〉||RD) and θ fiber (〈0 0 1〉||ND), and a simultaneous disappearance of the components of the γ fiber is observed. More details can be taken from Fig. 10 in which, besides the data of the α fiber and γ fiber, the η and the ε fibers are shown. The recrystallization texture in iron silicon is strongly dependent on the deformation texture and microstructure than on the recrystallization temperature [26,28] itself. The texture due to recrystallization and grain growth leads to a higher intensity spread along the 〈1 1 0〉||RD fiber than along the 〈1 1 1〉||ND fiber. 4.2. Two stage cold rolling with intermediate annealing After 75% cold rolling, the heavily deformed materials show a smooth type microstructure [21,22]. The microstructure after recrystallization at 600 1C shows equiaxed grains. After 60%
147
second cold rolling, the grains were elongated toward the rolling direction and after annealing the sample at 800 1C a polygonal shape of the grains was found (see Fig. 11). After 75% cold rolling a strong (0 0 1)[1 1 0] texture due to the 901 rotation around the ND of the previous hot rolling process can be seen. All 〈1 1 0〉||RD fibers are transferred to 〈1 1 0〉||TD as could be expected [23]. However, the intensity spreads along the α fiber 〈1 1 0〉||RD; particularly for the rotation cube component (0 0 1) [1 1 0], it was less than the results observed for samples after 90% cold rolling (see Figs. 8 and 12). Fig. 13 shows the texture evaluation of Fe–2.6% Si samples after a reduction of 75% by cold rolling and subsequent annealing at 600 1C/60 min. The results show a decrease of intensity for the α fiber 〈1 1 0〉||RD particularly for the rotation cube component (0 0 1) [1 1 0] while the intensity is spread along the γ fiber (〈1 1 1〉||ND), particularly the two components (1 1 1)[1 1 0] and (1 1 1)[1 1 2]. The Goss component (1 1 0)[1 0 0] is slightly increased after primary recrystallization.
TD
TD
RD
RD
TD
TD
RD
RD
Fig. 11. Optical micrographs of samples after (a) 75% cold rolling, (b) 600 1C/600 min (average grain size 19 μm), (c) 60% cold rolling (average grain size 133 μm) and (d) 800 1C/600 min (average grain size 75 mm).
RD
φ1 Ф
TD
110 Pmax= 3.8 mrd
Contours 1 3 6 9 12 16 F max = 16.2 mrd
Fig. 12. (a) The 110 pole figure and (b) ODF for 75% cold rolled sample at φ2 ¼ 01 and φ2 ¼451.
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RD φ1 Ф
TD
110 Pmax= 2.3 mrd
Contours 1 3 4 6 7 F max = 7.6 mrd
Fig. 13. (a) The 110 pole figure and (b) ODF for a sample after 600 1C/60 min at φ2 ¼01 and φ2 ¼ 451.
RD φ1 Ф
TD
110 Pmax= 2.3 mrd
Contours 1 3 4 6 F max = 5.6 mrd
Fig. 14. (a) The 110 pole figure and (b) ODF for a sample after 60% cold rolling at φ2 ¼01 and φ2 ¼ 451.
RD φ1 Ф
TD
110 Pmax= 2.2 mrd Contours 1 2 3 4 5 F max = 4.7 mrd Fig. 15. (a) The 110 pole figure and (b) ODF for a sample after 800 1C/60 min at φ2 ¼01 and φ2 ¼ 451.
The texture for the samples after a second cold rolling process with 60% reduction (Fig. 14) shows a more homogeneous increase in the intensity spread along the γ fiber (〈1 1 1〉||ND), especially for the two components (1 1 1)[1 1 0] and (1 1 1)[1 1 2]. At the same time a decrease in the intensity spread along the α fiber (〈1 1 0〉||RD) is shown. Fig. 15 shows the texture after the two stage cold rolling with intermediate annealing at 600 1C/60 min and further annealing at 800 1C/60 min. There is an increase of the intensity spread along the ε fiber (〈1 0 0〉||RD) particularly the two cube (0 0 1) [1 0 0] and Goss components [1 1 0]〈1 0 0〉 and more homogeneous intensity spread along the γ fiber (〈1 1 1〉||ND). More details are given
in Fig. 16 where, besides shown.
α and γ fibers, the η and the ε fibers are
5. Conclusions The cold rolling process plays a crucial role in the development of the crystallographic texture and magnetic properties of Fe–2.6%Si. It was observed that the two important components for soft magnetic materials, a cube component (0 0 1)[1 0 0] and a Goss component {1 1 0}〈0 0 1〉, can be produced by a two step cold rolling process with intermediate annealing. These components can also be
M.Z. Salih et al. / Journal of Magnetism and Magnetic Materials 362 (2014) 141–149
149
Fig. 16. The α, γ, η and ε fibers of the two stage cold rolling process.
developed in a one stage cold rolling process, but the magnetic properties are better after the two stage process. Additionally it was found that the larger grain size produced by high annealing temperature does not lead to better magnetic properties. Acknowledgment One of the authors (Mr. M.Z. Salih) would like to thank the Iraqi Ministry of Higher Education and Scientific Research (MOHESR) and Deutscher Akademischer Austausch Dienst (DAAD) for supporting his research. References [1] H.J. Bunge, C. Esling, Industrial applications of texture analysis, in: Advances and Applications of Quantitative Texture Analysis, eds. DGM-Informationsgesellschaft Oberursel, (1989), pp. 241–278. [2] H.J. Bunge, Texture and magnetic properties, Texture Microstruct. 11 (1989) 75–91. [3] L. Kestens, S. Jacobs, Texture control during the manfucturing of non-oriented electrical steels, Texture, Stress, Microstruct. (2008), http://dx.doi.org/10.1155/ 2008/173083. [4] M.Z. Quadir, B.J. Duggam, Acta Mater. 52 (2004) 4011–4021. [5] S. Nakaura, H. Homa, Mater. Sci. Forum 467–470 (2004) 269–274. [6] P. Gobermado, R. Detrov, D. Ruiz, E. leunis, L.A.I. Kestens, Texture evaluation in Si-alloyed ultra low-carbon steels after severe plastic deformation, Adv. Eng. Mater. 12 (2010) 1077–1081. [7] L. Seidel, M. Hölscher, K. Lücke, Rolling and recrystallization textures in iron– 3% Silicon, Textures Microstruct. 11 (1989) 171–185. [8] H.-G. Brokmeier, Physica B 234–236 (1997) 977–979.
[9] H.J. Bunge, Textures Microstruct. 10 (1989) 265–307. [10] H.-G. Brokmeier, Physica B 234–236 (1997) 1144–1145. [11] H.-G. Brokmeier, W.M. Gan, C. Randau, M. Völler, J. Rebelo-Kornmeier, M. Hofmann, Nucl. Instrum. Methods Phys. Res. A 642 (2011) 87–92. [12] M. Hofmann, R. Schneider, G.A. Seidle, J. Rebelo-Kornmeier, R.C. Wimpory, U. Garbe, H.-G. Brokmeier, Physica B 385–386 (2006) 1035–1037. [13] J. Tobisch, H.J. Bunge, The spherical sample method in neutron diffraction texture determination, Texture 1 (1972) 125–127. [14] C. Randau, U. Garbe, H.-G. Brokmeier, J. Appl. Crystallogr. 44 (2011) 641–646. [15] H.J. Bunge, H. Klein, Z. Metallkunde 87 (1996) 465–475. [16] H.J. Bunge, M. Dahms, The iterative series – expansion methode for quantitative texture analysis, J. Appl. Crystallogr. 22 (1989) 439–447. [17] M. Anhalt, B. Weidenfeller, Theoretical and experimental approach to characteristic measurement data of polymer bonded soft magnetic composites, J. Appl. Phys. 105 (2009) 113903. [18] R.M. Bozorth, Ferromagnetism, IEEE Press, New York, 1978. [19] B. Weidenfeller, W. Riehemann, Effects of surface treatments on the hysteresis losses of GO iron silicon steel, J. Magn. Magn. Mater. 292 (2005) 210–214. [20] B. Weidenfeller, W. Rieheman, Domain refinement and domain wall activation of surface treated Fe–Si sheets, J. Magn. Magn. Mater. 160 (1996) 136–138. [21] R. Kern, H.-P. Lee, H.J. Bunge, The rolling texture of iron of different purities, Steel Res. 57 (1986) 365–571. [22] R. Kern, Prakt. Metallogr. 21 (6) (1984) 273–293. [23] H. Inagaki, Stable end orientations in the rolling textures of the polycrystalline iron, Z. Metallkunde 78 (6) (1987) 431–439. [24] M.Z. Salih, B. Weidenfeller, N. Al-hamdany, H.-G. Brokmeier, W.M. Gan, Magnetic properties and crystallographic texture after 90% cold rolling plus different annealing on Fe–2.6% Si, J. Magn. Magn. Mater. 354 (2014) 105–111. [25] John J. Jonas, Transformation textures associated with steel processing, in: Proceedings of the Microstructure and Texture of Steel Conferences, 2008. [26] I. Saajdar, B. Verlinden, P. Van Houtte, ISIJ Int. 38 (7) (1998) 759–765. [27] G. Gottstein, K. Lücke, Tables for texture analysis of cubic crystals, in: Proceeding of the Fifth International Conference on Texture of Material, Achen, Germany, 1978. [28] P. Van Houtte, Manual of MTM-FHM, MTM-KULeuvent, Belgium, 1982.
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Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
The effect of intermediate annealing between cold rolled steps on crystallographic texture and magnetic properties of Fe–2.6% Si M.Z. Salih a,n, B. Weidenfeller c, N. Al-hamdany a, H.-G. Brokmeier a,b, W.M. Gan b a
Institut für Werkstoffkunde und Werkstofftechnik, TU Clausthal, Agricolastraße 6, D-38678 Clausthal-Zellerfeld, Germany Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, D-21502 Geesthacht, Germany c Institut für Elektrochemie, Abteilung für Materialwissenschaft, Arnold-Sommerfeld-Strasse 6, D-38678 Clausthal-Zellerfeld, Germany b
art ic l e i nf o
a b s t r a c t
Article history: Received 2 December 2013 Received in revised form 23 February 2014 Available online 17 March 2014
The crystallographic textures and magnetic properties of Fe–2.6 wt% Si after two different cold rolling and thermal treatment processes were investigated. The first set of samples was 90% cold rolled and annealed for 20 min at 600 1C, 700 1C, 900 1C and 1100 1C, while the second set was cold rolled for 75% and 60% with intermediate annealing at 600 1C for 60 min. Samples were analyzed by neutron diffraction and magnetic measurements. By means of the one and two stage cold rolling processes important cube (0 0 1)[1 0 0] and Goss components {1 1 0}〈0 0 1〉 were produced. Magnetic properties obtained through the two stage process were better than the properties found with the one stage process due to a higher fraction of the cube and Goss components in the material after the two stage process. An increase of grain sizes does not lead to better magnetic properties. & 2014 Elsevier B.V. All rights reserved.
Keywords: Electrical steel Hot rolling Cold rolling Intermediate annealing Magnetic property Neutron diffraction
1. Introduction Silicon steels are used in electrical machinery, like motors, generators and transformers. The magnetic materials used for technological applications can be divided into hard and soft magnetic materials. Hard magnetic materials are characterized by the highest possible energy product or the highest possible coercive force, whereas soft materials require the lowest coercive force or the highest permeability. All these properties are anisotropic and dependent on the texture in the polycrystalline state [1]. Iron based materials with the cube component (0 0 1)[1 0 0] provide the best soft magnetic properties such as high permeability, low power loss and low coercive force. This kind of texture can be obtained in Fe–Ni alloys. However, in Fe–Si alloys the cube component is difficult to produce while the Goss component (1 1 0)[0 0 1] is easier [1,2]. The improvement of texture for non-oriented electrical steels during thermo-mechanical processing can be attained by reducing the intensity of undesirable components such as α fiber (〈1 1 0〉//RD), γ fiber (〈1 1 1〉//ND), and {h h l}〈h/lþ1 h/lþ2 h/l〉 and increasing the fraction of spread along the η fiber (〈1 0 0〉//RD) and θ fiber (〈1 0 0〉//ND). These fibers are related to the macroscopic axis of the
n Correspondence to: Institut für Werkstoffkunde und Werkstofftechnik, Agricolastrasse 6, 38678 Clausthal-Zellerfeld, Germany. Tel.: þ49 4152 87 2635; fax: þ 49 4152 87 2666. E-mail address: [email protected] (M.Z. Salih).
http://dx.doi.org/10.1016/j.jmmm.2014.03.009 0304-8853/& 2014 Elsevier B.V. All rights reserved.
sample, defined as the rolling direction (RD), transverse direction (TD) and normal direction (ND) [3–6]. The two important components (0 0 1)[1 0 0] (cube) and {1 1 0}〈0 0 1〉 (Goss) can be obtained by hot rolling, cold rolling and cold rolling with intermediate heat treatments. There are two processes that can produce sheets with a Goss texture. The first one is cold rolling in two stages of about 70% and 50% reduction with intermediate annealing whereupon a hot band containing MnS precipitates is observed. In the second process a hot band containing additional AlN precipitates is subjected to cold rolling in one stage to about 85% followed by primary recrystallization [7]. The effects of the two different cold rolling processes of Fe–2.6% Si (one stage and two stages with various intermediate annealing processes) on the crystallographic texture and the magnetic properties are studied. The crystallographic texture was examined by neutron diffraction and the magnetic properties were measured using a hysteresis measurement system. Due to the coarse grain structure of the materials after annealing processes at high temperature high penetration and large beam cross section of neutron diffraction is an efficient tool for analysis of the bulk texture for these polycrystalline materials [8–10].
2. Materials An iron silicon alloy with 2.6 wt% silicon hot rolled at 1100 1C was provided by VACUUMESCHMELZE (Hanau, Germany) with a
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thickness reduction from about 330–380 mm to 10 mm. This corresponds to a reduction of approximately 97%. The chemical composition of the material (Table 1) was determined by electric discharge spectroscopy (Spectro Analytical Instrument, GmbH) after hot rolling. Samples of 25 mm 55 mm 10 mm were cut from the hot rolled band and afterward cold rolled on a laboratory mill (BÜHLER, Germany) to a final thickness of 1 mm along a direction perpendicular to the previous hot rolling direction (CRD? HRD). Reduction steps in the cold rolling processes were 0.1 mm/step. Two different rolling processes were used as shown schematically in Fig. 1.
2.1. Pole figure measurement The measurement of pole figures using neutrons was carried out using the materials science diffractometer (STRESS-SPEC) at the FRM2@MLZ (Garching, Germany) [11,12]. Fig. 2 shows a layout of the STRESS-SPEC with the sample mounted on the robot arm using the continuous scanning mode for intensity collection of complete pole figures. Continuous scanning is much faster than the step scan mode and allows, in parallel, the optimization of pole figure resolution on the grids. The sample dimensions for neutron measurements are 10 10 10 mm3. These dimensions increase the gage volume and improve the grain statistics which are needed for the coarse grained material after annealing. Therefore 10 slices were cut from the 1 mm thick sheet with a marked RD and glued together, using the spherical sample method of Tobisch and Bunge [13]. The average texture of the whole sample can be obtained by a large cross section of the beam, in our case 25 mm2 (see Fig. 3a). The measurements were carried out with a pyrolytic graphite monochromator (PG) and a monochromator take off angle which allows us to work with PG(004) and PG(006) planes. The main advantage in using two wavelengths is that the counting time in getting all needed pole figures with one detector setup is saved. The used area
detector of 300 300 mm² gave the Fe (1 1 0) reflection with PG(004) and Fe (2 0 0) and Fe (2 1 1) with PG(006) (Fig. 3b). The STRESS-SPEC diffractometer is equipped with a sample magazine which can be handled automatically by the robot enabling the measurement of all samples of each treatment without manual sample changing. Therefore, one of the advantages of this robot system is the operation of an automatic sample changer. Pole figure collection for one sample was done in about 1.2 h to get 72 readouts during continuous rotation and 6 tilt angles due to the detector size. The software package StressTextureCalculator (STeCa) [14] has been used to extract pole figure data from the area detector using the mathematical formulation of Bunge and Klein [15]. The Orientation Distribution Function (ODF) was calculated from three complete pole figures (1 1 0), (2 0 0) and (2 1 1) by ISEM (Iterative Series Expansion Method) up to a degree of series expansion Lmax ¼22 [16]. 2.2. Measurement of magnetic properties Samples for magnetic measurement were rectangular bars with a sample volume of 1 1 25 mm3. Measurements were conducted
Table 1 Results of the chemical composition of the used 97% hot rolled samples. Material
%Si
%C
%Mn
%S
%N
%Al
Fe–Si
2.6
0.0079
0.1135
0.0033
0.0065
0.001 Fig. 2. Stäubli RX160 robot with mounted sample.
hot rolling at 1100°C
Annealing at 800°C/ 60 min
Annealing at 600°C/ 60 min heating Cooling 4°C/ min 1.2°C/ min
heating 6°C/ min 75% cold rolling 200°C
200°C
60% cold rolling
Annealing at 1100°C/ 20 min
90% cold rolling
900°C/ 20 min 700°C/ 20 min 600°C/ 20 min
Fig. 1. Schematic presentation of the processing parameters.
Cooling 1.3°C/ min
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Diffracted
143
λ1= 1.8 Å 110
beam
Primary beam λ2= 1.2 Å 200
Samples
λ2= 1.2 Å 211
Fig. 3. (a) Schematic view of the measurement setup and (b) diffraction image with two wavelengths.
with a digital hysteresis recorder, described in detail elsewhere [17]. For purposes of comparability of the magnetic sample's properties, measurements have been conducted at identical polarizations and magnetizing frequencies by varying the magnetic field strength.
Table 2 Selected magnetic properties of the investigated samples which were cold rolled at one stage, cold rolled at two stages with an intermediate annealing process and annealed samples. Properties are measured in the rolling direction.
3. Results and discussion 3.1. Magnetic properties Table 2 shows variation of the magnetic properties of Fe–2.6% Si samples for one stage cold rolling and two stage cold rolling with an intermediate annealing process, measured at the magnetizing frequencies of 10 Hz and 50 Hz and a maximum polarization of J0 ¼1.8 T. The saturation polarization was estimated to be Js ¼ 2.04 T which corresponds to the values found in the literature for Fe–2.6% Si [18]. As can be seen in Table 2 power losses increase with frequency. This is due to an increase of classical and anomalous losses which are frequency dependent [18]. Relative to eddy currents in the sample the permeability is slightly decreased. Permeability values measured in the rolling direction of the as-received samples are nearly twice the values measured in the transversal direction. This indicates anisotropy of the grains oriented with magnetic easy axis in the rolling direction. Astonishingly the cold rolling process changes the permeability to higher values and simultaneously the power losses and coercive forces to lower values. Usually the rolling process induces many dislocations such that the permeability is decreased and coercive forces and power losses are increased. This is not the case here and therefore it can be assumed that the dislocation density in the asreceived material is similar to that in the material after the cold rolling process. Furthermore, these results lead to the assumption that the cold rolling process after the first hot rolling process causes a preferred crystallographic orientation of the grains resulting in better magnetic properties. This effect is higher for the 75% cold rolled materials than for the 90% cold rolled alloys. For one stage cold rolling the annealing process further increases the permeability values and decreases power losses and coercive forces. Regarding the values in Table 2 the thermal treatment of 20 min at 900 1C seems to lead to an optimum value in magnetic properties in the investigated range. According to Fig. 4 the mean grain size in such samples is around 122 μm. A further increase of the grain sizes by higher annealing temperatures does not lead to lower coercive force or power loss and higher permeability values although the number of imperfections in the material is reduced. This behavior is well known as the so-called Brown's paradoxon [19]. Impurities like dislocations and grain boundaries are sources for magnetic stray
As-received RD As-received TD
Permeability Power loss (kJ/m3)
Coercive force (A/m)
10 Hz 50 Hz 10Hz
50 Hz
10 Hz
50 Hz
76 47
74 46
3.1 1.3
11.76 2.42
435 155
1758 386
One stage cold rolling 90% Cold rolling 77 Annealing at 600 1C/20 min 89 Annealing at 700 1C/20 min 105 Annealing at 900 1C/20 min 112 Annealing at 1100 1C/20 min 49
76 89 101 112 49
3.1 1.31 1.01 0.74 0.98
4.21 2.39 2.02 1.43 2.70
420 148 142 101 113
640 366 329 269 401
Two stage cold rolling 75% Cold rolling Annealing at 600 1C/60 min 60% Cold rolling Annealing at 800 1C/60 min
93 122 82 130
2.89 1.32 2.96 1.1
3.62 2.23 3.57 1.86
323 171 420 108
526 355 570 266
92 116 84 121
fields. The energy stored in these magnetic stray fields can be reduced by the nucleation of domain walls. The higher number of magnetic domain walls leads to a reduction of power loss during magnetization reversal [20]. The two stages of cold rolling with an intermediate annealing process lead to an increase in the permeability values and simultaneously to a decrease of power losses and coercive forces. Regarding the values in Table 2 the annealing process at 800 1C/ 60 min shows the highest increase in the permeability and the biggest decrease in power losses and coercive forces compared to the other thermal annealing processes including the ones from the one stage cold rolling. According to Fig. 11, the mean grain size in such samples annealed at 800 1C/60 min is around 75 μm.
4. Texture 4.1. One stage cold rolling plus different annealing temperatures The main types of microstructures in the heavily deformed materials that could be related to different texture components include at first a “smooth” microstructure containing orientations between (0 0 1)[1 1 0] and (112)[1 1 0] with continuous orientation changes between neighboring areas. In this type, a continuous spread of (0 0 1)[1 1 0] toward (0 0 1)[1 0 0] exists. The second
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Fig. 4. Optical microscopy of (a) 97% hot rolled, (b) 90% cold rolled, (c) 600 1C/20 min (average grain size 19 mm) annealed, (d) 700 1C/20 min (average grain size 20 mm) annealed, (e) 900 1C/20 min (average grain size 122 mm) annealed and (f) 1100 1C/20 min (average grain size 354 mm) annealed samples.
Fig. 5. (a) φ2 ¼01 and (b) φ2 ¼ 451 ODF sections in Euler space showing the main texture components in steel.
type of microstructure consists of “grooved” regions, which are composed of orientations of the 〈1 1 1〉||ND family, mainly the orientation (1 1 1)[2 1 1] [21,22]. The microstructure of the hot rolled samples shows a mixture of smooth type and grooved type and changes after 90% cold rolling to smooth type in the heavily deformed material. The average grain sizes in the (rolling, transverse and normal) directions were calculated by the line intercept method and are given in Fig. 4. The microstructure after recrystallization shows coarse equiaxed grains as can be seen in Fig. 4. Furthermore, it can be seen that the texture changes after 90% cold rolling. The hot rolling components are rotated as was expected from the literature [23] and the cross rolling results in a very strong {0 0 1}〈1 1 0〉.
The most common texture components and orientation fibers in steel after rolling and recrystallization, which are shown in Fig. 5, are the φ2 ¼01and φ2 ¼ 451 sections of the ODF. According to the 451 section (see Fig. 5b), three different fibers (θ fiber 〈0 0 1〉||ND, α fiber 〈1 1 0〉||RD and γ fiber 〈1 1 1〉||ND) and also the Goss {1 1 0}〈0 0 1〉 component as shown in Fig. 6 can be observed. These fibers appeared due to the hot rolling processes [25]. Due to the cutting process of the 97% hot rolling sample the former RD becomes the TD and consequently the starting texture for cold rolling changes as shown in Fig. 7. The magnetic properties presented in Table 2 are related to the new sample orientation. It has to be noticed that the θ fiber 〈1 0 0〉||ND has not changed but the Goss component has changed. According to the ODF section
M.Z. Salih et al. / Journal of Magnetism and Magnetic Materials 362 (2014) 141–149
145
φ1
RD Ф
TD
Contours 1 2 3 5 F max = 6.0 mrd
110 Pmax= 2.7 mrd
Fig. 6. (a) (1 1 0) pole figure and (b) ODF for 97% hot rolling direction at φ2 ¼01 and φ2 ¼ 451.
RD φ1 Ф
TD
110 Pmax= 2.7 mrd
Contours 1 2 3 5 F max = 6.0 mrd
Fig. 7. (a) (1 1 0) pole figure and (b) ODF for as-received 901 rotated at ND at φ2 ¼ 01 and φ2 ¼451.
RD
φ1 Ф
TD
110 Pmax= 7 mrd
Contours 1 10 15 25 30 F max = 32.7 mrd
Fig. 8. (a) (1 1 0) pole figure and (b) ODF for 90% cold rolling at φ2 ¼ 01 and φ2 ¼451.
at φ2 ¼451 (see Fig. 5b) after rotated the sample 901 caused the position of Goss component is changed at the Euler angles of the orientation (φ1,Φ, φ2) (901, 901, 451) to the new position component (1 1 0)[1 1 0] at (01, 901, 451). During the cold rolling process the crystallite orientations which were primarily produced in the hot rolling process are rotated as expected [23]. Such a cross rolling procedure produces a very strong {0 0 1}〈1 1 0〉 texture, which can be seen in Fig. 8. It is developed due to a rotation of 901 around the ND. All 〈1 1 0〉 fibers parallel to the rolling direction are transferred into [1 1 0] fibers parallel to the transversal direction of the hot rolling step, and the
subsequent 90% cold rolling process finally converts them to a rotated cube component (0 0 1)[1 1 0] [24]. Fig. 9 shows the evolution of the texture after 90% cold rolling and subsequent annealing of the sample at different temperatures (600 1C, 700 1C, 900 1C and 1100 1C) for 20 min. During the primary recrystallization annealing at 600 1C, a homogeneous intensity spreads along the α fiber; the αn fiber and the γ fiber can be observed. After annealing of the sample at 700 1C, an intensity spreads along the α fiber higher than along the γ fiber, particularly increasing at the Euler angles of the orientation (φ1,Φ, φ2)E (15, 35, 45) that is visible. These angles correspond
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approximately to the (112)[7 11 2] set of miller indices [27]. This local maximum lies on a secondary fiber parallel to the α fiber (〈1 1 0〉||RD), running from the (1 1 1)[1 1 2] components to the
cube fiber. The annealing of the samples at 900 1C results in a high intensity spread along the α fiber and particularly a stronger intensity of the (1 1 2)[7 11 2]. The results also show that all the
600°C
700°C
900°C
1100°C
Fmax= 5.7 mrd Contours 1 2 3 5
Fmax= 7.6 mrd Contours 1 2 3 5 7
Fmax= 12.3 mrd Contours 1 2 4 8 10 12
Fmax= 8.5 mrd Contours 1 2 3 5 7 9
φ2 = 0°
φ2= 45°
Fig. 9. Annealing texture of one stage cold rolling process by φ2 ¼ 01 and φ2 ¼451 ODF sections after annealing at 600 1C, 700 1C, 900 1C and 1100 1C for 20 min.
Fig. 10. The α, γ, η and ε fibers of the one stage cold rolling process after annealing at 600 1C, 700 1C, 900 1C and 1100 1C for 20 min.
M.Z. Salih et al. / Journal of Magnetism and Magnetic Materials 362 (2014) 141–149
components that have spread along the γ fiber diminished and only the (1 1 1)[1 1 2] component has appeared. An annealing of the samples at 1100 1C leads to a significant increase of the intensity spread along the α fiber (〈1 1 0〉||RD) and θ fiber (〈0 0 1〉||ND), and a simultaneous disappearance of the components of the γ fiber is observed. More details can be taken from Fig. 10 in which, besides the data of the α fiber and γ fiber, the η and the ε fibers are shown. The recrystallization texture in iron silicon is strongly dependent on the deformation texture and microstructure than on the recrystallization temperature [26,28] itself. The texture due to recrystallization and grain growth leads to a higher intensity spread along the 〈1 1 0〉||RD fiber than along the 〈1 1 1〉||ND fiber. 4.2. Two stage cold rolling with intermediate annealing After 75% cold rolling, the heavily deformed materials show a smooth type microstructure [21,22]. The microstructure after recrystallization at 600 1C shows equiaxed grains. After 60%
147
second cold rolling, the grains were elongated toward the rolling direction and after annealing the sample at 800 1C a polygonal shape of the grains was found (see Fig. 11). After 75% cold rolling a strong (0 0 1)[1 1 0] texture due to the 901 rotation around the ND of the previous hot rolling process can be seen. All 〈1 1 0〉||RD fibers are transferred to 〈1 1 0〉||TD as could be expected [23]. However, the intensity spreads along the α fiber 〈1 1 0〉||RD; particularly for the rotation cube component (0 0 1) [1 1 0], it was less than the results observed for samples after 90% cold rolling (see Figs. 8 and 12). Fig. 13 shows the texture evaluation of Fe–2.6% Si samples after a reduction of 75% by cold rolling and subsequent annealing at 600 1C/60 min. The results show a decrease of intensity for the α fiber 〈1 1 0〉||RD particularly for the rotation cube component (0 0 1) [1 1 0] while the intensity is spread along the γ fiber (〈1 1 1〉||ND), particularly the two components (1 1 1)[1 1 0] and (1 1 1)[1 1 2]. The Goss component (1 1 0)[1 0 0] is slightly increased after primary recrystallization.
TD
TD
RD
RD
TD
TD
RD
RD
Fig. 11. Optical micrographs of samples after (a) 75% cold rolling, (b) 600 1C/600 min (average grain size 19 μm), (c) 60% cold rolling (average grain size 133 μm) and (d) 800 1C/600 min (average grain size 75 mm).
RD
φ1 Ф
TD
110 Pmax= 3.8 mrd
Contours 1 3 6 9 12 16 F max = 16.2 mrd
Fig. 12. (a) The 110 pole figure and (b) ODF for 75% cold rolled sample at φ2 ¼ 01 and φ2 ¼451.
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RD φ1 Ф
TD
110 Pmax= 2.3 mrd
Contours 1 3 4 6 7 F max = 7.6 mrd
Fig. 13. (a) The 110 pole figure and (b) ODF for a sample after 600 1C/60 min at φ2 ¼01 and φ2 ¼ 451.
RD φ1 Ф
TD
110 Pmax= 2.3 mrd
Contours 1 3 4 6 F max = 5.6 mrd
Fig. 14. (a) The 110 pole figure and (b) ODF for a sample after 60% cold rolling at φ2 ¼01 and φ2 ¼ 451.
RD φ1 Ф
TD
110 Pmax= 2.2 mrd Contours 1 2 3 4 5 F max = 4.7 mrd Fig. 15. (a) The 110 pole figure and (b) ODF for a sample after 800 1C/60 min at φ2 ¼01 and φ2 ¼ 451.
The texture for the samples after a second cold rolling process with 60% reduction (Fig. 14) shows a more homogeneous increase in the intensity spread along the γ fiber (〈1 1 1〉||ND), especially for the two components (1 1 1)[1 1 0] and (1 1 1)[1 1 2]. At the same time a decrease in the intensity spread along the α fiber (〈1 1 0〉||RD) is shown. Fig. 15 shows the texture after the two stage cold rolling with intermediate annealing at 600 1C/60 min and further annealing at 800 1C/60 min. There is an increase of the intensity spread along the ε fiber (〈1 0 0〉||RD) particularly the two cube (0 0 1) [1 0 0] and Goss components [1 1 0]〈1 0 0〉 and more homogeneous intensity spread along the γ fiber (〈1 1 1〉||ND). More details are given
in Fig. 16 where, besides shown.
α and γ fibers, the η and the ε fibers are
5. Conclusions The cold rolling process plays a crucial role in the development of the crystallographic texture and magnetic properties of Fe–2.6%Si. It was observed that the two important components for soft magnetic materials, a cube component (0 0 1)[1 0 0] and a Goss component {1 1 0}〈0 0 1〉, can be produced by a two step cold rolling process with intermediate annealing. These components can also be
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149
Fig. 16. The α, γ, η and ε fibers of the two stage cold rolling process.
developed in a one stage cold rolling process, but the magnetic properties are better after the two stage process. Additionally it was found that the larger grain size produced by high annealing temperature does not lead to better magnetic properties. Acknowledgment One of the authors (Mr. M.Z. Salih) would like to thank the Iraqi Ministry of Higher Education and Scientific Research (MOHESR) and Deutscher Akademischer Austausch Dienst (DAAD) for supporting his research. References [1] H.J. Bunge, C. Esling, Industrial applications of texture analysis, in: Advances and Applications of Quantitative Texture Analysis, eds. DGM-Informationsgesellschaft Oberursel, (1989), pp. 241–278. [2] H.J. Bunge, Texture and magnetic properties, Texture Microstruct. 11 (1989) 75–91. [3] L. Kestens, S. Jacobs, Texture control during the manfucturing of non-oriented electrical steels, Texture, Stress, Microstruct. (2008), http://dx.doi.org/10.1155/ 2008/173083. [4] M.Z. Quadir, B.J. Duggam, Acta Mater. 52 (2004) 4011–4021. [5] S. Nakaura, H. Homa, Mater. Sci. Forum 467–470 (2004) 269–274. [6] P. Gobermado, R. Detrov, D. Ruiz, E. leunis, L.A.I. Kestens, Texture evaluation in Si-alloyed ultra low-carbon steels after severe plastic deformation, Adv. Eng. Mater. 12 (2010) 1077–1081. [7] L. Seidel, M. Hölscher, K. Lücke, Rolling and recrystallization textures in iron– 3% Silicon, Textures Microstruct. 11 (1989) 171–185. [8] H.-G. Brokmeier, Physica B 234–236 (1997) 977–979.
[9] H.J. Bunge, Textures Microstruct. 10 (1989) 265–307. [10] H.-G. Brokmeier, Physica B 234–236 (1997) 1144–1145. [11] H.-G. Brokmeier, W.M. Gan, C. Randau, M. Völler, J. Rebelo-Kornmeier, M. Hofmann, Nucl. Instrum. Methods Phys. Res. A 642 (2011) 87–92. [12] M. Hofmann, R. Schneider, G.A. Seidle, J. Rebelo-Kornmeier, R.C. Wimpory, U. Garbe, H.-G. Brokmeier, Physica B 385–386 (2006) 1035–1037. [13] J. Tobisch, H.J. Bunge, The spherical sample method in neutron diffraction texture determination, Texture 1 (1972) 125–127. [14] C. Randau, U. Garbe, H.-G. Brokmeier, J. Appl. Crystallogr. 44 (2011) 641–646. [15] H.J. Bunge, H. Klein, Z. Metallkunde 87 (1996) 465–475. [16] H.J. Bunge, M. Dahms, The iterative series – expansion methode for quantitative texture analysis, J. Appl. Crystallogr. 22 (1989) 439–447. [17] M. Anhalt, B. Weidenfeller, Theoretical and experimental approach to characteristic measurement data of polymer bonded soft magnetic composites, J. Appl. Phys. 105 (2009) 113903. [18] R.M. Bozorth, Ferromagnetism, IEEE Press, New York, 1978. [19] B. Weidenfeller, W. Riehemann, Effects of surface treatments on the hysteresis losses of GO iron silicon steel, J. Magn. Magn. Mater. 292 (2005) 210–214. [20] B. Weidenfeller, W. Rieheman, Domain refinement and domain wall activation of surface treated Fe–Si sheets, J. Magn. Magn. Mater. 160 (1996) 136–138. [21] R. Kern, H.-P. Lee, H.J. Bunge, The rolling texture of iron of different purities, Steel Res. 57 (1986) 365–571. [22] R. Kern, Prakt. Metallogr. 21 (6) (1984) 273–293. [23] H. Inagaki, Stable end orientations in the rolling textures of the polycrystalline iron, Z. Metallkunde 78 (6) (1987) 431–439. [24] M.Z. Salih, B. Weidenfeller, N. Al-hamdany, H.-G. Brokmeier, W.M. Gan, Magnetic properties and crystallographic texture after 90% cold rolling plus different annealing on Fe–2.6% Si, J. Magn. Magn. Mater. 354 (2014) 105–111. [25] John J. Jonas, Transformation textures associated with steel processing, in: Proceedings of the Microstructure and Texture of Steel Conferences, 2008. [26] I. Saajdar, B. Verlinden, P. Van Houtte, ISIJ Int. 38 (7) (1998) 759–765. [27] G. Gottstein, K. Lücke, Tables for texture analysis of cubic crystals, in: Proceeding of the Fifth International Conference on Texture of Material, Achen, Germany, 1978. [28] P. Van Houtte, Manual of MTM-FHM, MTM-KULeuvent, Belgium, 1982.